Heat exchange in wet capillary-porous bodies of various compositions during convective heating in vapor-air media

Abstract

The results of the study of the heating process of wet capillary-porous bodies of various compositions (meat products) during heat treatment in dry air and steam-air mixture under conditions of forced circulation of the heating medium are presented. The studies were carried out on a moist fat-free sample (chicken fillet meat) and a low-moisture fat sample (pork shoulder blade) formed in the form of a cylinder and a plate. It is shown that the process of heating of meat products of various compositions obeys the laws of the theory of unsteady thermal conductivity of homogeneous bodies, despite the variety of accompanying phase and physico-chemical transformations. It is established that the regular mode of non-stationary thermal conductivity occurs at Fo ≥ 0.2 for all the studied variants. Based on the processing and analysis of experimental data, criterion equations of the form Θ = f(Fo,Bi) for the central layer of the studied products in the temperature range 160–240 °C were obtained. It has been established that the peculiarities of heating of meat products in a vapor-air mixture environment lead to lower values of the coefficients μ1 and N(Bi) at regular operation compared with heating in dry air. It was found that low-moisture fatty samples are characterized by lower values of μ1 and N(Bi) in comparison with moist fat-free ones. As a result of comparison with tabular data for solids, it is shown that the experimental coefficients μ1 and N(Bi) are characterized by lower values for all the studied variants. It is established that the nature of the change in N(Bi) and μ1 for solids and the studied products is opposite, i.e., with an increase in the number of Bi, an increase in N(Bi) and μ1 is characteristic for solids, while their decrease is characteristic for the studied products. The practical significance of the research consists in improving the quality characteristics of minced meat products and optimizing operational production planning through the use of the methodology of predictive calculation of the duration of thermal operations.